The present disclosure relates to catalyst compositions with an external electron donor comprising one or more of the following: a phosphite, a phosphonite, a pyrophosphite (diphosphite), and/or a diphosphazane (iminodiphosphite), and the resultant olefin-based polymers produced therefrom.
Known are Ziegler-Natta catalyst compositions for the production of olefin-based polymers. Ziegler-Natta catalyst compositions typically include a procatalyst containing a transition metal halide (i.e., titanium, chromium, vanadium), a cocatalyst such as an organoaluminum compound, and optionally an external electron donor and/or an activity limiting agent. The art presently recognizes a finite set of compounds suitable for use as external electron donors. With the continued diversification and sophistication of applications for olefin-based polymers, the art recognizes the need for olefin-based polymers with improved and varied properties. Desirable would be external electron donors for Ziegler-Natta catalyst compositions that contribute to strong catalyst activity and high hydrogen response during polymerization. Further desired are external electron donors for Ziegler-Natta catalysts that produce propylene-based polymers with high isotacticity, high melt flow rate, and low toxicity.